Full carbon soles are the stiffest, lightest option available, and they're fantastic for competitive road racing where every watt of power matters. They transfer your pedaling energy with virtually no flex, which is why pros and serious racers love them. But for most recreational riders, they're probably more than you need.
The trade-off is comfort and walkability. Full carbon soles have zero give, which can feel harsh on long rides or if you have foot issues. They're also terrible for walking — think slippery coffee shop floors and awkward off-bike moments. If you're doing group rides, centuries, or commuting where you occasionally dismount, a carbon-reinforced or nylon sole will feel much friendlier.
Save full carbon for the race scene. If you're not competing or chasing PRs, you'll get better value and everyday comfort from a less aggressive sole material.